Chassis flex in NB8A

[93_Clubman]

Believe the following is one of mx589 (of this forum) Gumtree ads - looks like he might have what you're after: https://www.gumtree.com.au/s-ad/altona/ ... 1171544612

[CoachOz]

delrin is plastic. Whether delrin makes a difference is probably not proven i.e. if you replace worn originals with new originals does it improve / so replacing with a hard plastic is that the right choice. Why did not the Mazda engineers use delrin ,bearing in mind that the engineers could have specified delrin in the first place. All oem parts are specced out and selected as the right choice.

I have an BB and it does not flap like an MG TC or a TR4 and it has not been modified so maybe and quite probably HKS is right. What does it matter if there is a little movement ( i.e. not so bad that a door cannot be opened). I always thought that screwing lumps of metal onto chassis rails is over the top and introduces holes and gaps where moisture can cause future corrosion . One of the great things about an MX-5 is how well it rides- supple and good roadholding for road use.

So maybe just do one thing and see what happens.

An 8A has a less rigid chassis than the 8B and therefore less torsional rigidity. Having had both, the difference is significant, which is why I'm trying to stiffen the 8A up.

[trader]

the last thing I put on my NA were delrin door bushings. I put them on to try and stop door rattles. they certainly allow a Volvo type closing feel as they are a tighter fit than OEM. As far as body flex was concerned they did nothing in my view. Maybe this is because I had already had new bushes all around, front and rear NB bracing, strip bracing under the doors and NB bracing across the seats. Each time I did something I noticed improvement but not with the door bushes. Maybe I Had gone as far as possible before I put them in. I'd consider that worn bushes are creating bash and crash rather than body flex.

[Code4]

I have an NB8A I use for cruising and weekends away with the Minister for War and Finance, so have a serious interest in making mine NVH free.
1) Suspension in good working order.
2) Suitable tyres. 15" Michelin PS3's is as performance orientated as I would go. Going to try 14'' soon. Had 16x7's and Hankook tyres that were shocking.
3) DEFINANTLY the Automotive Plus Torque Box roll bar. I have the twin hoop. Looks great and it mounts to more places than just the parcel shelf. Removed all NVH from the rear half of my car.

About to try some basic aftermarket bracing for the front half soon.
Not sure if you will remove all flex, but you can change the harmonics to be quieter.

[pley3r]

On my 8a chassis rails (without the cross peices) and fender braces made the biggest difference to mine.

If you can find a wrecked newer model grab the newer underbody braces. Got all 3 for $10 i cut down the center one so its just a cross body brace as there is no mounting points for the 'x' bars behind it.

Strut tower and parcel shelf bars probably help but not obvious.

Door bushings made no difference to mine, just a pain in the ass to open the door so took them off.

Plus good suspension.
Mine will lift a wheel on a big enough curb lol.

[StillIC]

The only elements I have which could possibly stiffen my NA6 chassis are an AGI half cage (which does nothing to stiffen it torsionally, from the seat of the pants scuttle shake test), and my own design 3D printed door bushes. The door bushes made a huge reduction to scuttle shake but did take a bit of setting up to get just right. That is, I filed them down to match the inside dimension of the door striker as closely as possibly (press fit), then fitted them so they were in exactly the correct position so the door would shut without too much resistance. I also added some adhesive foam to the outside to fill the gap between the 3rd side of the striker and the bush to prevent the door rattling in the open/closed direction (which was audible and annoying).b

[wasp47]

IMHO ,the factory uses "rubber" because they are terrified of noise and harshness, I know there is a term for it but I have brain fade
Cheers
Steven

[93_Clubman]

NVH (noise, vibration & harshness)

[StillIC]

IMHO ,the factory uses "rubber" because they are terrified of noise and harshness, I know there is a term for it but I have brain fade
Cheers
Steven

The factory fits the rubber ones because they have only 53 seconds or less to do the fitment. A well fitted, press fit, hard plastic bush takes about half an hour of fiddling about to make it work just right. It has to be matched to the cup dimension and put in exactly the right spot...and still there is resistance when closing the door. But the stiffness, oh the stiffness!

The rubber version can fit the cup whatever the tolerance, and be put in slightly the wrong place, the door is easy to open and close and NVH is not too bad...arguably. Shame about the scuttle shake.

[CoachOz]

I see that there will be some fiddling to do when my door bushes arrive and hopefully they'll make a difference

[KevGoat]

There is some initial fiddling to get them properly aligned due to less tolerance as StillIC mentions. I also had to dremel out the holes on mine to gain enough adjustment to allow the door to close flush to the body but most don't seem to have to do this. It's well worth the effort though.

[twr7cx]

I fitted the Beavis Motorsport door bushes. Just fitted them loosely, opened and closed the doors a few times to get them in place, tightened them up and opened and closed again to check. Done.

Being an 89 NA6 I've also fitted a front and rear brace similar to that which later NA's and NBs have standard.

I have OBX frame rails and butterfly brace in a box on my garage floor waiting to be fitted. Got the for $600.00 brand new from eBay USA.

I did look at the Frog Arms/Strong Arms but Keith from Flyin' Miata advised they were only beneficial for high horse power vehicles. So I decided I didn't need the extra weight or lighter wallet.

I'm currently looking at roll bars so enjoyed the above discussions.